History of Remote Sensing: In the Beginning; Launch Vehicles

History of Remote Sensing: In the Beginning; Launch Vehicles

The photographic camera has served as a prime remote sensor for more than 150 years. It captures an image of targets exterior to it by concentrating electromagnetic (EM) radiation (normally, visible light) through a lens onto a recording medium. A key advance in photography occurred in 1871 when Dr. Henry Maddox, a Brit, announced development of a photographic negative made by enclosing silver halide suspended in an emulsion mounted on a glass plate. Silver halide film remains the prime recording medium today. The film displays the target objects in their relative positions by variations in their brightness of gray levels (black and white) or color tones.

Although the first, rather primitive photographs were taken as "stills" on the ground, the idea photographing the Earth's surface from above, yielding the so-called aerial photo, emerged in the 1860s with pictures from balloons. The first success - now lost - is a photo of a French Valley made by Felix Tournachon.

Several famous kite photos were taken of the devastation in San Francisco, California right after the 1906 earthquake that, together with fire, destroyed most of the city.

It appears that Wilbur Wright - the co-developer of the first aeroplane to leave the ground in free flight - himself was the first to take pictures from an airplane, in France in 1908 and Italy in 1909.

By the first World War, cameras mounted on airplanes, or more commonly held by aviators, provided aerial views of fairly large surface areas that were invaluable for military reconnaissance.

From then until the early 1960s, the aerial photograph remained the single standard tool for depicting the surface from a vertical or oblique perspective.

Historically, the first photos taken from a small rocket, from a height of about 100 meters, were imaged from a rocket designed by Alfred Nobel (of Prize fame) and launched in 1897 over a Swedish landscape.

A camera succeeded in photographing the landscape at a height of 600 meters (2000 ft) reached by Alfred Maul's rocket during a 1904 launch:
Remote sensing above the atmosphere originated at the dawn of the Space Age. The power and capability of launch vehicles was a big factor in determining what remote sensors could be placed as part (or all) of the payload. At first, by 1946, some V-2 rockets, acquired from Germany after World War II, were launched by the U.S. Army in April 1946.

Smaller sounding rockets, such as the Wac Corporal, and the Viking and Aerobee series, were developed and launched by the military in the late '40s and '50s. These rockets, while not attaining orbit, contained automated still or movie cameras that took pictures as the vehicle ascended.

The other frequently used launch vehicle is the Space Transport System (STS), more commonly known as the Space Shuttle. It uses two external fuel tanks plus its own engines.

Remote sensing Satellites.

The first non-photo sensors were television cameras mounted on unmanned spacecraft and were devoted mainly to looking at clouds. The first U.S. meteorological satellite, TIROS-1, launched by an Atlas rocket into orbit on April 1, 1960, looked similar to this later TIROS vehicle.

TIROS, for Television Infrared Observation Satellite, used vidicon cameras to scan wide areas at a time.

Then, in the 1960s as man entered space, astronauts in space capsules took photos out the window. In time, the space photographers had specific targets and a schedule, although they also have some freedom to snap pictures at targets of opportunity.

Earlier on, other types of sensors were developed that " took images using the EM spectrum beyond the visible, into the near and thermal infrared regions. The field of view (FOV) was broad, usually 100s of kilometers on a side. Such synoptic areas of regional coverage were of great value to the meteorological community, so that many of these early satellites were metsats, dedicated to gathering information on clouds, air temperatures, wind patterns, etc.

In order to take advantage of and make good use of remote sensing data, we must be able to extract meaningful information from the imagery. This brings us to the topic of discussion in this chapter - interpretation and analysis - the sixth element of the remote sensing process which we defined in Chapter 1. Interpretation and analysis of remote sensing imagery involves the identification and/or measurement of various targets in an image in order to extract useful information about them. Targets in remote sensing images may be any feature or object which can be observed in an image, and have the following characteristics:

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  Targets may be a point, line, or area feature. This means that they can have any form, from a bus in a parking lot or plane on a runway, to a bridge or roadway, to a large expanse of water or a field.
  
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  The target must be distinguishable; it must contrast with other features around it in the image.